Hydro-thermal coupled behaviors in free zones and matrix of porous media: insights from a micro-continuum transport approach

The intricate coupling of seepage and thermal behaviors in fractured rock masses is highly significant because it affects geological stability and geothermal extraction, and is vital for predicting subsurface fluid and heat flow for sustainable management of underground resources. In this study, a two-phase Darcy–Brinkman–Stokes method is extended to describe hydrothermal behaviors of fractured soils and rocks. Such an extension makes up for the limitations of previous studies on seepage in rock and soil medium. A novel solver, hybridPorousInterHTFoam, is then developed to simulate such hydro-thermal behaviors in the fractured rock mass. The applicability of the coupled numerical model and corresponding solver is validated by simulating a well-designed experiment. By conducting various numerical simulations, the influence of important factors such as seepage velocity, aperture, conduits shape, and fracture roughness on heat transfer efficiency within fractured rock is investigated. The findings emphasize the substantial control exerted by fluid velocity and fracture aperture on heat transfer within rock masses while demonstrating that fracture roughness has no significant effect on heat transfer with seepage. Additionally, the shape, number, and distribution of conduits contribute to the heat transfer process with seepage in three-dimensional rock masses.